1. Field of the Invention
The present invention relates to a spindle motor and the like used in a magnetic disc and an optical disc.
2. Description of the Related Art
Magnetic discs and the optical discs are becoming higher in speed and capacity year after year. Thus, high speed, high torque as well as low vibration and low noise are required for a spindle motor for driving the disc.
Rewritable DVD, for example, often performs writing at a maximum speed of about 6000 r/min, and since slight vibration of the disc may lead to a writing error, low vibration is especially required for the spindle motor driving the disc.
A method of reducing vibration of a spindle motor (particularly reducing vibration in a direction of thrust) includes a method of reducing vibration by providing a permanent magnet on either a rotor side or a stator side to attract a rotor in the direction of thrust with the permanent magnet, and suppressing lifting off of a shaft.
Another method includes a method of forming a shaft with a magnetic material and attracting the end face of the shaft with the permanent magnet. However, such method is not usually used in actual products. (Refer to JP 52-095010A and JP 05-068363A, for example).
In the former method of providing a permanent magnet on either a rotor side or a stator side and attracting a rotor in the direction of thrust with the permanent magnet, attracting force can be easily made stronger since the attracting surface area can be made larger. However, in order to secure a sufficient attracting force, a large permanent magnet needs be used, which increases the cost for the permanent magnet.
In the latter method of attracting a shaft with a permanent magnet, the attracting surface area is small and thus a sufficient attracting force is not obtained in many cases, resulting in that this method is seldom used.